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TOPIC: Extrasolar Planets


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Study says every star has planets

Every star twinkling in the night sky plays host to at least one planet, a new study suggests.
That implies there are some 10 billion Earth-sized planets in our galaxy.
Using a technique called gravitational microlensing, an international team found a handful of exoplanets that imply the existence of billions more.

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Planets around stars are the rule rather than the exception

An international team, including three astronomers from the European Southern Observatory (ESO), has used the technique of gravitational microlensing to measure how common planets are in the Milky Way. After a six-year search that surveyed millions of stars, the team concludes that planets around stars are the rule rather than the exception. The results will appear in the journal Nature on 12 January 2012.
Over the past 16 years, astronomers have detected more than 700 confirmed exoplanets and have started to probe the spectra and atmospheres of these worlds. While studying the properties of individual exoplanets is undeniably valuable, a much more basic question remains: how commonplace are planets in the Milky Way?

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The Milky Way Contains at Least 100 Billion Planets

Our Milky Way galaxy contains a minimum of 100 billion planets according to a detailed statistical study based on the detection of three extrasolar planets by an observational technique called microlensing.
Kailash Sahu, of the Space Telescope Science Institute in Baltimore, Md., is part of an international team reporting today that our galaxy contains a minimum of one planet for every star on average. This means that there is likely to be a minimum of 1,500 planets within just 50 light-years of Earth.

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Caltech-Led Team of Astronomers Finds 18 New Planets

Discoveries of new planets just keep coming and coming. Take, for instance, the 18 recently found by a team of astronomers led by scientists at the California Institute of Technology (Caltech).
Using the Keck Observatory in Hawaii - with follow-up observations using the McDonald and Fairborn Observatories in Texas and Arizona, respectively - the researchers surveyed about 300 stars. They focused on those dubbed "retired" A-type stars that are more than one and a half times more massive than the sun. These stars are just past the main stage of their life - hence, "retired" - and are now puffing up into what's called a subgiant star.

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Title: Warm Spitzer Photometry of XO-4b, HAT-P-6b and HAT-P-8b
Authors: Kamen O. Todorov, Drake Deming, Heather A. Knutson, Adam Burrows, Pedro V. Sada, Nicolas B. Cowan, Eric Agol, Jean-Michel Desert, Jonathan J. Fortney, David Charbonneau, Gregory Laughlin, Jonathan Langton, Adam P. Showman, Nikole K. Lewis

We have analysed Warm Spitzer/IRAC observations of the secondary eclipses of three planets, XO-4b, HAT-P-6b and HAT-P-8b. We measure secondary eclipse amplitudes at 3.6{\mu}m and 4.5{\mu}m for each target. XO-4b exhibits a stronger eclipse depth at 4.5{\mu}m than at 3.6{\mu}m, which is consistent with the presence of a temperature inversion. HAT-P-8b shows a stronger eclipse amplitude at 3.6{\mu}m, and is best-described by models without a temperature inversion. The eclipse depths of HAT-P-6b can be fitted with models with a small or no temperature inversion. We consider our results in the context of a postulated relationship between stellar activity and temperature inversions and a relationship between irradiation level and planet dayside temperature, as discussed by Knutson et al. (2010) and Cowan & Agol (2011), respectively. Our results are consistent with these hypotheses, but do not significantly strengthen them. To measure accurate secondary eclipse central phases, we require accurate ephemerides. We obtain primary transit observations and supplement them with publicly available observations to update the orbital ephemerides of the three planets. Based on the secondary eclipse timing, we set upper boundaries for e cos(\omega) for HAT-P-6b, HAT-P-8b and XO-4b and find that the values are consistent with circular orbits.

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Weirdest Planets



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Title: Know the Star, Know the Planet. II. Speckle Interferometry of Exoplanet Host Stars
Authors: Brian D. Mason, William I. Hartkopf, Deepak Raghavan, John P. Subasavage, Lewis C. Roberts Jr., Nils H. Turner, Theo A. ten Brummelaar

A study of the host stars to exoplanets is important to understanding their environment. To that end, we report new speckle observations of a sample of exoplanet host primaries. The bright exoplanet host HD 8673 (= HIP 6702) is revealed to have a companion, although at this time we cannot definitively establish the companion as physical or optical. The observing lists for planet searches and for these observations have for the most part been pre-screened for known duplicity, so the detected binary fraction is lower than what would otherwise be expected. Therefore, a large number of double stars were observed contemporaneously for verification and quality control purposes, to ensure the lack of detection of companions for exoplanet hosts was valid. In these additional observations, ten pairs are resolved for the first time and sixty pairs are confirmed. These observations were obtained with the USNO speckle camera on the NOAO 4m telescopes at both KPNO and CTIO from 2001 to 2010.

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Interstellar crashes could throw out habitable planets

Our solar system, where planets have a range of sizes and move in near-circular paths, may be rather unusual, according to a German-British team led by Professor Pavel Kroupa of the University of Bonn. The astronomers, who publish their model in the journal Monthly Notices of the Royal Astronomical Society, find that forming planetary systems may be knocked around by crashes with nearby clumps of material, leading to systems where planets have highly inclined orbits and where the smaller (and potentially habitable) worlds are thrown out completely.
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New planets feature young star and twin Neptunes

An international team, including Oxford University scientists, has discovered ten new planets. Amongst them is one orbiting a star perhaps only a few hundred million years old, twin Neptune-sized planets, and a rare Saturn-like world.
The planets were detected using the CoRoT (Convection, Rotation and Transits) space telescope, operated by the French space agency CNES. It discovers planets outside our solar system - exoplanets - when they 'transit', that is pass in front of their stars.
The new finds were announced on 14 June at the Second CoRoT Symposium, held in Marseille.
Out of the ten new exoplanets (CoRoT-16b through to 24b and c) seven are hot Jupiters some of which are unusually dense and/or on unusually elongated orbits, and one is in orbit around an unusually young star. The announcement also includes a planet slightly smaller than Saturn, and two Neptune-sized planets orbiting the same star.

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Title: Defining and cataloguing exoplanets: The exoplanet.eu database
Authors: Jean Schneider, Cyrill Dedieu, Pierre Le Sidaner, Renaud Savalle, Ivan Zolotukhin

We describe an online database for extra-solar planetary-mass candidates, updated regularly as new data are available. We first discuss criteria for the inclusion of objects in the catalogue: "definition" of a planet and several aspects of the confidence level of planet candidates. {We are led to point out the conflict between sharpness of belonging or not to a catalogue and fuzziness of the confidence level.} We then describe the different tables of extra-solar planetary systems, including unconfirmed candidates (which will ultimately be confirmed, or not, by direct imaging). It also provides online tools: histogrammes of planet and host star data, cross-correlations between these parameters and some VO services. Future evolutions of the database are presented.

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